[Spectral study of some polyoxovanadium borates].

Four novel polyoxovanadium borates with [(VO)12O6B18O42], namely (enH2)6 H3 [(VO)12O6B18O42].13H2O(1), [Ni (en)2]6 H3 [(VO)12 O6B18O42].8H2O(2), [Cu(en)2]5 H3 [(VO)12 O6B18 O42] [B(OH)3]2. 16H20(3) and(enH2)4 Na4H3 [(VO)12 O6B18O42].8H2O(4), were synthesized. The relationship between their properties and structures were studied by using FTIR, UV-Vis DRS and fluorescence etc. Among these compounds, compound (1) possesses isolated [(VO)12O6B18O42] cage, there is a ring of B18O42 sandwiched between two vanadium-oxygen clusters V6O18 by eighteen B--(micro3--O)--V bonds, while compound (2) is rather six [Ni(en)2], each connected with the B18O42 ring by two Ni--(micro3--O)--B. In compounds (3) and (4), the anion clusters [(VO)12 O6B18O42]13- are connected with [Cu(en)2]2+ and Na+ , respectively. Thus, the compounds (3) and (4) are extended to an infinite two-dimensional network structure, respectively. These characteristic vibrational frequencies of polyoxovanadium borates are related to the structures of these compounds. In UV/Vis DRS spectra, there are two characteristic peaks of polyoxometalates at 205 and 260 nm, respectively. The fluorescence spectra of these four compounds have been studied, and they have emission peaks at 415 nm excited by 310 nm which are caused by Omicro-->Mo. The fluorescence lifetimes of these compounds have been studied.